Seamless call switching in a dual mode environment

ABSTRACT

Methods and apparatus for providing a seamless switching of voice calls between different wireless networks are disclosed. In one illustrative example, a mobile communication device has a processor and one or more wireless transceivers coupled to the processor. The one or more wireless transceivers include a first transceiver portion operative in accordance with a first wireless network (e.g. a GSM/GPRS cellular network) and a second transceiver portion operative in accordance with a second wireless network (e.g. an 802.11 wireless network). A voice call is maintained between the mobile device and a communication terminal through call control equipment. The processor of the mobile device is operative to maintain voice communications for the voice call over a traffic channel established between the mobile device and the first wireless network using the first transceiver portion; cause a connecting call to be established with the communication terminal through the call control equipment in response to a predetermined condition, where the connecting call involves a traffic channel established between the second wireless network and the mobile device using the second transceiver portion; and after the connecting call is established, maintain voice communications for the voice call over the traffic channel established between the second wireless network and the mobile device.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority to U.S.Non-Provisional Patent Application entitled “Seamless Call Switching InA Dual Mode Enviroment” having Ser. No. 10/992,934 and a filing date of19 Nov. 2004, which further claims priority to U.S. Provisional PatentApplication entitled “Seamless Call Switching In A Dual ModeEnvironment” having Ser. No. 60/523,644 and a filing date of 20 Nov.2003.

BACKGROUND

1. Field of the Technology

The present application relates generally to seamlessly switchingbetween different wireless networks during a voice call involving amobile communication device which is compatible with these wirelessnetworks.

2. Description of the Related Art

In the field of wireless communications, the problem of seamlesslyswitching communications between two incompatible wireless networks fora mobile communication device has not been adequately addressed.

One major issue is how to switch between two different wireless networkswithout dropping an active call, such as a voice call, involving themobile device. In an exemplary situation, the mobile device may hecompatible with both GSM/GPRS technologies and 802.11 technologies butyet be unable to seamlessly switch between these networks during activecalls. This switching would need to take place without dropping theactive call and, preferably, without letting either party know that theswitching has taken place.

SUMMARY

Methods and apparatus for providing a seamless switching of voice callsbetween different wireless networks are described herein. In oneillustrative example, a mobile communication device has a processor andone or more wireless transceivers coupled to the processor. The one ormore wireless transceivers include a first transceiver portion operativein accordance with a first wireless network (e.g. GSM/GPRS cellularnetwork) and a second transceiver portion operative in accordance with asecond wireless network (e.g. 802.11 wireless network). That is, themobile device is a dual-mode device.

A voice call is maintained between the mobile device and a communicationterminal through call control equipment. The processor of the mobiledevice is operative to maintain voice communications for the voice callover a traffic channel established between the mobile device and thefirst wireless network using the first transceiver portion; cause aconnecting call to be established with the communication terminalthrough the call control equipment based on a predetermined condition,where the connecting call involves a traffic channel established betweenthe second wireless network and the mobile device using the secondtransceiver portion; and after the connecting call is established,maintain voice communications for the voice call over the trafficchannel established between the second wireless network and the mobiledevice.

In one embodiment, the one or more processors of the mobile device causethe connecting call to be established by causing a network switchingmessage to be sent to the call control equipment; receiving a callinitiation message from the second wireless network for the connectingcall in response to sending the network switching message; and causing acall answering message to be sent to the second wireless network basedon receiving the call initiation message from the second wirelessnetwork, for thereby establishing the traffic channel between the secondwireless network and the mobile device.

Other aspects and features of the present application will becomeapparent to those ordinarily skilled in the art upon review of thefollowing description of specific embodiments of the present inventionin conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present application will now be described, by way ofexample only, with reference to the attached figures. Same referencenumerals are used in different figures to denote similar elements.

FIG. 1 is an illustration of a call control center located in acarrier's network infrastructure for handling call routing issues;

FIG. 2 is an illustration of a call control center located within acorporation for handling call routing issues;

FIG. 3 is an illustration of a mobile device roaming away from an 802.11hot spot where the call control center located within a wirelessnetwork;

FIG. 4 is an illustration of a mobile device roaming away from an 802.11corporate access point where the call control center located within thecorporation; and

FIG. 5 is an illustration of a data flow diagram that supports themobile device's behaviour when roaming from one network to another;

FIG. 6 is a flowchart for describing the mobile device method ofproviding the seamless switching of networks for voice calls;

FIG. 7 is a flowchart for describing the call control equipment methodof providing the seamless switching of networks for voice callsinvolving the mobile device;

FIG. 8 is an illustration of one of the wireless communication networkswithin which the mobile device may communicate, where the wirelessnetwork is a GSM/GPRS based cellular telecommunications network;

FIG. 9 is a schematic block diagram of a mobile device in a specific andpreferred implementation as a mobile station; and

FIG. 10 is a block diagram illustration of pertinent components of callcontrol equipment for use in the present application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Methods and apparatus for providing a seamless switching of voice callsbetween different wifeless networks are described herein. In oneillustrative example, a mobile communication device has a processor andone or more wireless transceivers coupled to the processor. The one ormore wireless transceivers include a first transceiver portion operativein accordance with a first wireless network (e.g. GSM/GPRS cellularnetwork) and a second transceiver portion operative in accordance with asecond wireless network (e.g. 802.11 wireless network). Thus, the mobiledevice is a dual-mode wireless device. A voice call may be maintainedbetween the mobile device and a communication terminal through callcontrol equipment. The processor of the mobile device is operative tomaintain voice communications for the voice call over a traffic channelestablished between the mobile device and the first wireless networkusing the first transceiver portion; cause a connecting call to beestablished with the communication terminal through the call controlequipment in response to a predetermined condition, where the connectingcall involves a traffic channel established between the second wirelessnetwork and the mobile device using the second transceiver portion; andafter the connecting call is established, maintain voice communicationsfor the voice call over the traffic channel established between thesecond wireless network and the mobile device. In one embodiment, theone or more processors of the mobile device cause the connecting call tobe established by causing a network switching message to be sent to thecall control equipment; receiving a call initiation message from thesecond wireless network for the connecting call in response to sendingthe network switching message; and causing a call answering message tobe sent to the second wireless network based on receiving the callinitiation message from the second wireless network, for therebyestablishing the traffic channel between the second wireless network andthe mobile device.

Turning to FIG. 1 there is shown a system for handling the seamlessswitching of voice calls for a mobile communication device 100. In theembodiment of FIG. 1, call control equipment 112 is located in acarrier's network infrastructure for handling call control. The basicarchitecture for call control equipment 112 is shown later in relationto FIG. 10. In FIG. 1, mobile device 100 is shown to operate in a firstwireless network 102, which is a wide area wireless network such as acellular telecommunications network. For example, the first wirelessnetwork 102 may be a Global Systems for Mobile Communications (GSM) andGeneral Packet Radio Service (GPRS) based network. A router 110 routesand connects outside calls 120 to mobile device 100 with the help of thesubcomponent referred to as the call control equipment 112. In thisembodiment, router 110 resides within, or in close proximity to, thecarrier's network. Router 110 may be a wired or wireless router and,preferably, router 110 is a wireless router.

Second wireless network 106 is different from first wireless network102; that is, the networks 102 and 106 support different wirelesscommunication technologies and protocols. To one skilled in the art,this second wireless network 106 may support one several different typesof networks including cellular networks and non-cellular networks. Thesenetworks may include, but are not limited to, those based on CodeDivision Multiple Access (CDMA), CDMA2000, Universal MobileTelecommunications Services (UMTS), iDEN, and Bluetooth. Preferably,however, second wireless network 106 is an 802.11 based network locatedin a “hot spot”. In the present application, the 802.11 network may bereferred to as a wireless local area network (WLAN). WLANs are typicallywire-connected to the Internet using traditional Telco connections toprovide higher bandwidth data communications for mobile devices. A WLANtypically operates in accordance with IEEE or ETSI standards, forexample, although any suitable communication technologies may beutilized. Second wireless network 106 is connected to a wide areanetwork (WAN) 108, such as the Internet, to which call control equipment112 is also connected. Preferably, second wireless network 106 andmobile device 100 support Voice over Internet Protocol (VoIP) voicecommunications. In a primary embodiment described herein, mobile device100 maintains a preference for using second wireless network 106 (i.e.the local area network or 802.11 WLAN) over first wireless network 102(i.e. the wide area cellular network) and attempts to utilize it forcommunications whenever possible.

Mobile device 100 may be on a voice call with a communication terminal(not shown in FIG. 1) over first wireless network 102. This voice callis established through or by call control equipment 112. During thevoice call, mobile device 100 may be moved 104 between first wirelessnetwork 102 and a second wireless network 106. As mobile device 100reaches second wireless network 106, it detects the hot spot throughcoverage indicators and protocol handshakes, techniques that are wellknown in the art. In response, mobile device 100 may send a message 114to call control equipment 112 upon entry into the hot spot area. Themessage indicates that mobile device 100 has entered within range of asupportable 802.11 hot spot. The message may further indicate that thevoice call and any data routing mechanism should be “shifted” to the newnetwork. Alternatively, the transition may be made by manual userintervention. In any case, if network switching is performed, cost andspeed savings may be achieved by using the 802.11 network instead of thewide-area GSM/GPRS network.

In an alternate technique, mobile device 100 delays for a time periodduring which coverage and/or registration in second wireless network 106is maintained before causing the transition. This time period ismonitored with use of a timer. If the connection with second wirelessnetwork 106 fails during this time period, mobile device 100 refrainsfrom causing any transition (e.g. refrains from sending the message) andthe timer is reset. If coverage and/or registration with second wirelessnetwork 106 is re-established, mobile device 100 again delays for thetimer period before causing the transition. Preferably, the mobiledevice delays for a time period greater than 1 minute. Alternatively,time period is greater than 30 seconds, such as between about 30 secondsand 2 minutes.

For transitioning between the networks, call control equipment 112silently places a second call to mobile device 100. This second callinvolves the communication terminal involved in the initial voice callwith mobile device 100 in a conference call type connection. As mobiledevice 100 is expecting this second call because it initiated therequest, mobile device 100 may silently and seamlessly accept thissecond call. Mobile device 100 then switches its audio paths from thefirst call to the second call. Preferably, the VoIP communications isutilized in the 802.11 hot spot area for this call. Note that thetransition may be done in a gradual fashion where audio signals fromboth calls are first mixed and gradually increased/decreased in volumeuntil the complete transition is made; alternatively the transition isabrupt where there is little if any overlap of the audio. The signal 114may be sent over Session Initiation Protocol (SIP) through an IPv6network link to call control equipment 112. Alternatively, the solutionoperates in connection with traditional technology and data, linksavailable and operating in wireless data networks. Therefore, thistechnique requires neither SIP nor IPv6 to operate, although it iscompatible with these technologies if they were present.

Stability of the new (second) call is ensured over time so that, theoriginal (first) call may be released. That is, the mobile device 100delays for a time period during which the second call is maintainedbefore causing the first call to be released. The time period ismonitored through use of a timer. If the second call fails during thistime period, mobile device 100 maintains the first call and the timer isreset. If the second call is reattempted, mobile device 100 again delaysfor the timer period before releasing the first call. Preferably, themobile device delays for a time period greater than 1 minute.Alternatively, time period is greater than 30 seconds, such as betweenabout 30 seconds and 2 minutes.

The call splitting functionality of call control equipment 112 may beachieved in a few different ways. One known useful component is providedby OnRelay of the United Kingdom. A technology component called a MobileBranch Exchange (MBX) from OnRelay is a server that resides adjacent toa Public Branch Exchange (PBX). This MBX takes a copy of an incomingcall and rings a cell phone number at the same time as an associateddesk phone, enabling the end user to pick up the call in eitherlocation. Similarly, for mobile originated calls, the MBX receives thecall information as a Short Message Server (SMS) message, places a callto the mobile and to the called party, making the called party thinkthat the call is originating from the user's desk phone. One feature ofthe MBX is that a user may be on a mobile device call and, when the usergets back to his/her desk phone, may pick up the desk phone and releasethe mobile device call—similar to switching phones in the samehousehold. MBX in its current form may handle either conventional orIP-based PBX systems. It has been developed solely for use in a PBXenvironment and routing/bridging calls between PBXs and mobile phones.

Other technology components, especially those enabling mobile“dual-mode” communications and mobile VoIP, may be utilized to achieveoptimized results for the present techniques. Specifically, optimizedfeatures include (1) expanded call control features, either through SIPor some other mechanism, allowing the interfacing to an 802.11 networkat the same time as controlling a PBX; alternatively a separate 802.11access point (AP) could be used and call control center 112 couldinterface directly to it; (2) the presence of dual-mode handsets; (3) acentral control and command infrastructure to access calls and data andto route to either network as necessary; (4) communicating ‘out-of-band’to the mobile device 100 while maintaining a phone call. Specifically,for example, Qualcomm announced the implementation of both WCDMA (a.k.a.UMTS) and GSM calls with a mobile device using a radioOne™ directconversion RF dual-mode solution technology. The mobile device utilizedan integrated MSM6200(™) Mobile Station Modem (MSM™) chipset solution,consisting of the MSM6200 UMTS/GSM/GPRS baseband modem, RFL6200™ andRFR620™ WCDMA receivers, RTR6200™ GSM transceiver with WCDMAtransmitter, and PM6050™ power management device. In addition, a companycalled Spectralink of Boulder, Colo., U.S.A., makes Voice over IP (VoIP)telephony technology using 802.11-based handset phones. This technologycomponent allows owners of traditional PBX phone systems in anenterprise business take advantage of VoIP phones. A NetLink PRI Gatewayconnects to PBX phone systems that have a trunked ISDN primary rateinterface (PRI) so it may support several mobile devices simultaneously.The gateway, in turn, connects to the wired network and on to the accesspoints (APs) that talk to the VoIP handsets.

Turning now to FIG. 2, there is shown an illustration of call controlcenter 112 being located within a corporation 124. A second wirelessnetwork 118 within or adjacent corporation 124 is a wireless 802.11 LANsometimes termed a “Wi-Fi” network. These wireless LAN solutions are nowcommonly supported within such corporations 124. Companies are currentlyusing wireless LAN solutions to support the campus-wide demand for anIntranet 122 within corporation 124. Once connected to the Intranet 122,access to company resources becomes possible. Naturally, the secondwireless network 118 is seen as bridging a firewall 116 protection ofthe corporation 124 (if any), most corporations are currently addressingthese security problems today where applicable.

An initial voice call is either received or placed by mobile device 100.For calls placed from mobile device 100, the desire to place a call issignalled to call control equipment 112, which then simultaneouslyplaces the voice call to mobile device 100 and the communicationterminal that the end user of mobile device 100 desires to call. In thisway, call control equipment 112 retains control of the voice call at alltimes. As mobile device 100 moves from first wireless network 102 (e.g.GSM/GPRS) to second wireless network 118 (e.g. 802.11 wireless LAN), thevoice call is initially maintained in GSM/GPRS. Note that the 802.11transceiver portion on mobile device 100 operates independently of theGSM/GPRS transceiver portion on the same mobile device 100.

Next, mobile device 100 uses 802.11 to send a signal 114 through secondwireless network 118. Signal 114 instructs call control equipment 112 toplace another call to mobile device 100 through the 802.11 network. Thissecond call involves the communication terminal involved in the initialvoice call with mobile device 100 in a conference call type connection.Thus, as mobile device 100 moves onto campus and locks onto secondwireless network 118, mobile device 100 messages call control equipment112 to place the second call to mobile device 100 over second wirelessnetwork 118. Call control equipment 112 may either perform this functiondirectly or request the PBX to connect the additional call, depending onthe specific design of call control equipment 112. Once mobile device100 has the new call, it merges it with the existing voice call,performs a final check to ensure that the new call is of adequatequality, and then terminates the GSM/GPRS call.

As described, this changeover may be performed automatically by mobiledevice 100 with or without being governed by algorithms that detect a“constant and clean” 802.11 signal corresponding to second wirelessnetwork 118. For example, if a signal is detected that has a signalquality of ‘X’, for a period of‘N’ minutes, then the second call may bewarranted. Thus, mobile device 100 delays for a time period during whichcoverage and/or registration in second wireless network 118 ismaintained before causing the transition. This time period is monitoredwith use of a timer. If the connection with second wireless network 118fails during this time period, mobile device 100 refrains from causingany transition (e.g. retrains from sending the message) and the timer isreset. If coverage and/or registration with second wireless network 118is reestablished, mobile device 100 again delays for the timer periodbefore causing the transition. Preferably, the mobile device delays fora time period greater than 1 minute. Alternatively, time period isgreater than 30 seconds, such as between about 30 seconds and 2 minutes.Using an alternative technique, no automatic transitioning is performedby mobile device 100 but rather mobile device 100 visually displays anoption for or choice between networks for the end user. The end user mayselect the new second network which causes the transition.

Either mobile device 100 or call control equipment 112 may control theprocess of determining at what point in time to drop the merged call. Inone embodiment, mobile device 100 is better situated to determine howlong to hold the two calls and to understand the conditions needed to beable to drop the first call. In another embodiment, there is greaterelegance for call control equipment 112 to handle dropping the initialcall, for example, by maintaining a timer. Once the second call isprimary to mobile device 100, call control center 112 may seamlesslydrop the original call portion. Thus, stability of the new (second) callis ensured over time so that the original (first) call may be released.That is, the mobile device 100 delays for a time period during which thesecond call is maintained before causing the first call to be released.The time period is monitored through use of a timer. If the second callfails during this time period, mobile device 100 maintains the firstcall and the timer is reset. If the second call is reattempted, mobiledevice 100 again delays for the timer period before releasing the firstcall. Preferably, the mobile device delays for a time period greaterthan 1 minute. Alternatively, time period is greater than 30 seconds,such as between about 30 seconds and 2 minutes.

Turning now to FIG. 3, there is shown an illustration of mobile device100 heading away from an 802.11 hot spot where call control center 112is located within second wireless network 106. All elements of thesolution are identical to FIG. 1, except for mobile device 100 is nowmoving away from the 802.11 hotspot. This scenario is more complicatedthen that described in relation to the previous figures as mobile device100 is slowing losing coverage and voice quality. Mobile device 100maintains 802.11 coverage as long as possible, as this is the cheapestand fastest communication method. As coverage fails, mobile device 100may send a signal to call control equipment 112 automatically or througha user request. Mobile device 100 uses first wireless network 102(GSM/GPRS) to send signal 114 as this should be more reliable. Callcontrol equipment 112 then places a second call to mobile device 100over first wireless network 102. This second call involves thecommunication terminal involved in the initial voice call with mobiledevice 100 in a conference call type connection. As described inrelation to the previous figures, mobile device 100 quietly receivesthis second call, and may merge the two calls similar to a conferencecall connection. Shortly thereafter, the first call is dropped and theuser is left with the call through first wireless network 102. Notethat, in this embodiment, it is possible that the end user might have toforce early termination of the first call if static and voice qualitydrops too quickly. This could result in a small delay or detection bythe other party that a transition has occurred.

Turning now to FIG. 4, there is shown an illustration of mobile device100 heading away from an 802.11 corporate access point (AP) where callcontrol center 112 is located within the corporation 124. The elementsshown in FIG. 4 are similar to FIG. 2 except that mobile device 100 ismoving away from second wireless network 118. In this scenario, mobiledevice 100 detects a reduced signal from second wireless network 118, orthe user invokes a menu that allows them to control network switching(e.g. they realize they are leaving the 802.11 campus area). As in FIG.3, signal 114 is communicated over the first wireless network 102 as thereliability should be higher. When the message is received by callcontrol equipment 112, it issues a second call over first wirelessnetwork 102 to mobile device 100. This second call involves thecommunication terminal involved in the initial voice call with mobiledevice 100 in a conference call type connection. Mobile device 100 thenanswers the call, preferably silently without disruption, and merges thetwo calls similar to a conference call. After a period of time (e.g. inthe range of seconds or less), mobile device 100 or call controlequipment 112 drops die original call in favor of the second call overfirst wireless network 102.

A voice call 120 may also be received on or placed to mobile device 100using a voice over IP (VoIP) method on the 802.11 network 118. Callcontrol equipment 112 retains control of the voice call 120 at alltimes. As the caller's connection to second wireless network 118 startsto fade (or a handover is initiated by the caller through the push of abutton on the mobile device 100), mobile device 100 signals 114 throughsecond wireless network 118 to instruct call control equipment 112 toinitiate a call over first wireless network 102. Mobile device 100, withknowledge that an incoming call is imminent and the number the call iscoming from, silently accepts the call and authenticates it as ahandover of the current call over second wireless network 118. Fromhere, the two calls are merged (similar to a conference call). Once itsconfirmed that the new call is stable and ready, mobile device 100 orcall control equipment 112 drops the 802.11 call, and the new GSM/GPRScall is maintained. Neither party on the phone detects any mode changetaking place assuming both 802.11 quality of service is acceptable andGSM/GPRS reception is good. Note that there is always at least one callsession active on mobile device 100 at any given point of time.

In an alternative embodiment, where mobile device 100 hits a dramatic“falling off” of 802.11 coverage, call control equipment 112 intervenesand automatically switches the call over first wireless network 102(GSM/GPRS). In this situation, call control equipment 112 may noticethat data intended for mobile device 100 fails to be delivered, or thatthe call has been dropped on the 802.11 network. In this case, the callis automatically moved over to the wide-area GSM/GPRS network forrecovery. To assist with interruption, call control equipment 112 mayinform the other party by audio that they will be reconnectedmomentarily while initiating an outbound GSM/GPRS connection to mobiledevice 100. Alternatively, mobile device 100 may initiate the resumptionof the call over GSM/GPRS by detecting the unintentional loss of the802.11 call and immediately sending a “resume” call packet over theGSM/GPRS network to call control equipment 112. This message may be asimple datagram using proprietary protocols or a SIP-based message asalready discussed.

Turning to FIG. 5, there is shown an illustration of a data flow diagramsupporting the mobile device's behavior when moving from one network toanother. In step 200, the user and mobile device are moving andeventually a transition stage is reached. This is a stage where mobiledevice is in coverage of two different networks. If the user detects achange (step 202), perhaps either in voice quality or by knowledge of analternative network option, they may act on such situations. Thealternative network could be a less expensive option like 802.11 orBluetooth, or they might be leaving an 802.11 network shortly and wantto return to their wide-area GSM/GPRS network connection. If the userdesires to change the network, the user may invoke a menu and requestthe network change directly through the user interface (step 204).

If the mobile device detects a change in step 204, either throughreduced coverage parameters, or in the arrival of a new networkconnection with higher priority, it may decide to make a change. Anetwork may have a different priority due to a better cost or speed. Ifthe mobile device does not detect that a change is needed or possible instep 204, then it is loss of the call that determines that somethingmust be done. When the call is dropped in step 208, either the user actson the problem or the call control equipment detects the problem andacts. If the user detects the call is lost and decides to act at step208, the user may select a menu item on the mobile device to request thecall be re-routed to an alternative network (step 210). In an exemplarysituation, the user has just left an 802.11 network and coverage on thewide-area GSM/GPRS network was initially too weak to support a call.Then, within seconds, the coverage improves and the call is routed tothe mobile device before the other party drops off.

If the call control equipment detects that the call has dropped in step208, it places a call to the mobile device to open a new call through analternative network connection (step 212). If configured and selected bythe user, a message may be played for the other caller (step 214). Whenthe call is completed the calls are bridged or connected together (step215). Referring back to the step 206, where the mobile device detectsthe change in network coverage, or after the user selects a menu tochange networks at steps 204 and 210, a signal is next sent to the callcontrol equipment (step 216). In response, the call control equipmentbridges or connects the calls together (step 218), similar to aconference call connection. After a certain length of time during whichthe new call is stable, the first call is dropped (step 220).

FIG. 6 is a flowchart which describes a method for use by a mobilecommunication device in switching voice calls between two differentwireless communication networks. This method may be performed in theenvironment(s) described in relation to FIGS. 1-4, with the mobiledevice shown and described later in relation to FIGS. 9-10. Note thatalthough the method describes the transition from a first wirelessnetwork to a second wireless network, the same or similar techniques maybe utilized for transitioning from the second wireless network to thefirst wireless network. The steps are performed by one or morecontrollers or processors (e.g. a microprocessor and/or DSP) of themobile device, in connection with any other necessary device components(e.g. its RF transceiver portions). As apparent from this methoddescription, the call control equipment performs a complimentary method(see FIG. 7) associated with the mobile device method. A computerprogram product, of the present application may include a storage medium(e.g. FLASH memory) and computer instructions stored in the storagemedium which are executed by the one or more processors for performingsuch methods. In this method, the mobile device has a first transceiverportion which operates in accordance with a first wireless network (e.g.GSM/GPRS cellular network) and a second transceiver portion whichoperates in accordance with a second wireless network (e.g. 802.11wireless network). Preferably, Voice over IP (VoIP) communications isutilized through one of the wireless networks (e.g. the 802.11 network)for a lower cost alternative. Note further that the mobile device may beassociated with at least two different unique identifiers (e.g.telephone number, mobile telephone number, and/or IP address) forimplementing the method. As an example, the mobile device may publish orprovide only a corporate enterprise telephone number for others tocontact the mobile device. When dialed by an outside caller, thistelephone number call always gets routed to the call control equipment,which causes the mobile device to be alerted to the incoming call withinthe enterprise (e.g. the call control equipment using the telephonenumber or IP address of the mobile device via the 802.11 network) and/oroutside the enterprise (e.g. the call control equipment using the mobiletelephone number of the mobile device via the cellular network).

Beginning at a start block 602 of FIG. 6, the mobile device maintainsvoice communications for a voice call established between the mobiledevice and a communication terminal through the first wireless network(step 604 of FIG. 6). This call is facilitated through the call controlequipment. From the perspective of the mobile device, the voice callinvolves one or more traffic channels established between the firstwireless network and the mobile device using the first transceiverportion. During the voice call, the mobile device causes a connectingcall to be established with the call control equipment (step 606 of FIG.6). This connecting call involves the communication terminal involved inthe initial voice call with the mobile device in a conference call typeconnection. In addition, the connecting call involves one or moretraffic channels established between the second wireless network and themobile device using the second transceiver portion. Subsequently, themobile device maintains voice communications for the voice call over thetraffic channel established between the second wireless network and themobile device (step 608 of FIG. 6). Note that the call control equipmentcauses the voice communications of the voice call through the firstwireless network to be replicated in the connecting call through thesecond wireless network, so that the mobile device simultaneouslymaintains the voice communications for the voice call through both thefirst and the second wireless networks.

The mobile device may cause the connecting call of step 606 to beestablished in a number of different ways. In one embodiment, the mobiledevice initially causes a network switching message to be sent to thecall control equipment upon detection of a predetermined condition. Inthis case, the mobile device subsequently receives a call initiationmessage (e.g. a page message for a call) from the second wirelessnetwork for the connecting call that is sent in response to the networkswitching message. In response to the call initiation message, themobile device answers the connecting call by causing a call answeringmessage (e.g. a page response message) to be sent to the second wirelessnetwork, which thereby establishes the one or more traffic channelsbetween the second wireless network and the mobile device. In analternative embodiment, the call control equipment initiates theconnecting call without the need to receive any network switchingmessage from the mobile device. In yet another alternative embodiment,the mobile device is the entity that initiates the connecting call tothe call control equipment by sending a call initiation message to thesecond wireless network, where the call control equipment automaticallyanswers the connecting call.

Either way, the mobile device “automatically” and “silently” performsthe activities necessary in step 606 of FIG. 6 for calling or answeringthe connecting call. Put another way, the activities in step 606 may beperformed by the mobile device so as to be transparent to the end user.Alternatively, the mobile device may cause a user input prompt to bevisually displayed in its visual display (or invoke a “call ringing” atthe mobile device) for end user selection of whether the alternative(second) wireless network should be utilized. If the alternativewireless network is selected by the end user, the mobile device causesthe connecting call to be established with the call control equipment.If the alternative wireless network is not selected by the end user, themobile device does not cause the connecting call to be established withthe call control equipment (i.e. the mobile device remains on the firstwireless network).

As indicated earlier, the connecting call of step 606 may be establishedin response to identifying a predetermined condition. The predeterminedcondition may be, for example, a poor signal condition between themobile device and the first wireless network (e.g. the 802.11 wirelessnetwork). As another example, the predetermined condition may be apredetermined signal detection of the second wireless network (e.g thelocal area 802.11 wireless network). That is, the mere detection of theavailability of the second wireless network may be sufficient for theestablishment of the connecting call with the call control equipment. Asyet another example, the predetermined condition may be a user inputsignal detected at the mobile device. Specifically, the mobile devicemay visually display a user input prompt or an option (e.g. pop-up inputprompt) for the end user to select the alternative (second) wirelessnetwork when it becomes available; the end user selection of this optionis the user input signal which triggers the connecting call to the callcontrol equipment. Note that the predetermined condition is preferablyidentified and acted upon at the mobile device, but may alternatively beidentified and acted upon at the call control equipment.

The mobile device may delay for a time period during which coverageand/or registration in second wireless network (e.g. 802.11) ismaintained before causing the transition. This time period is monitoredwith use of a timer. If the connection with second wireless networkfails during this time period, the mobile device refrains from causingany transition (e.g. refrains from sending the message) and the timer isreset. If coverage and/or registration with second wireless network isre-established, the mobile device again delays for the timer periodbefore causing the transition. Preferably, the mobile device delays fora time period greater than 1 minute. Alternatively, time period isgreater than 30 seconds, such as between about 30 seconds and 2 minutes.Similarly, stability of the new (second) call may be ensured over timeso that the original (first) call may be released. That is, the mobiledevice delays for a time period during which the second call ismaintained before causing the first call to be released. The time periodis monitored through use of a timer. If the second call fails duringthis time period, the mobile device maintains the first call and thetimer is reset. If the second call is reattempted, the mobile deviceagain delays for the timer period before releasing the first call.Preferably, the mobile device delays for a time period greater than 1minute. Alternatively, time period is greater than 30 seconds, such asbetween about 30 seconds and 2 minutes.

Depending on the specific implementation, at some point in time themobile device may completely switch its audio paths (speaker andmicrophone) from the one or more traffic channels with the firstwireless network to the one or more traffic channels with the secondwireless network. This may be done in a quick and abrupt fashion or,alternatively, in a gradual fashion where the audio signals of bothcalls are first mixed and then subsequently gradually decreased involume (to/from the first wireless network) and correspondinglyincreased in volume (to/from the second wireless network) until fullyswitched. Such techniques may be performed by the mobile device oralternatively by the call control equipment. At some point in time, themobile device may cause the connection portion of the voice call fromthe call control equipment to the mobile device through the firstwireless network to be terminated. When this happens, the one or moretraffic channels with the first wireless network are terminated. Thismay be done by sending a suitable message to the call control equipment,for example, through the first wireless network. Alternatively, the callcontrol equipment may initiation the termination of the connectionportion of the original call.

FIG. 7 is a flowchart which describes a method for use by call controlequipment in switching voice calls for a mobile device between twodifferent wireless networks. This method may be performed in theenvironment(s) described in relation to FIGS. 1-4. Note that althoughthe method describes the transition from a first wireless network to asecond wireless network, the same or similar techniques may be utilizedfor transitioning from the second wireless network to the first wirelessnetwork. The steps are performed by computer instructions executed byone or more controllers or processors (e.g. a microprocessor) of a callcontrol server of the call control equipment. The basic architecture forcall control equipment 112 is shown later in relation to FIG. 10. Asapparent from this method description, the mobile device performs acomplimentary method (see FIG. 6) associated with the call controlmethod. A computer program product of the present application mayinclude a storage medium (e.g. memory) and computer instructions storedin the storage medium which are executed by the one or more processorsfor performing such methods. Preferably, Voice over IP (VoIP)communications is utilized through one of the wireless networks (e.g.the 802.11 network) for a lower cost alternative. Note that the mobiledevice may be associated with at least two different unique identifiers(e.g. telephone number, mobile telephone number, and/or IP address) forthe method. As an example, the mobile device may publish or provide onlya corporate enterprise telephone number for others to contact thedevice. When dialed, this telephone number always gets routed to thecall control equipment which causes the mobile device to be alerted tothe incoming call within the enterprise (e.g. with use of the telephonenumber or IP address of the mobile device via the 802.11 network) and/oroutside the enterprise (e.g. with use of the mobile telephone number ofthe mobile device via the cellular network).

Beginning at a start block 702 of FIG. 7, the call control equipmentfacilitates the establishment of a voice call between the mobile deviceand a communication terminal through the first wireless network (step704 of FIG. 7). From the perspective of the mobile device, the voicecall involves one or more traffic channels established between the firstwireless network and the mobile device. During the voice call, the callcontrol equipment causes a connecting call to be established with themobile device (step 706 of FIG. 7). This connecting call involves thecommunication terminal involved in the initial voice call with themobile device in a conference call type connection. In addition, theconnecting call involves one or more traffic channels establishedbetween the second wireless network and the mobile device. The callcontrol equipment connects or bridges the connecting call with the voicecall so that voice communications may be maintained over the trafficchannel between the second wireless network and the mobile device (step708 of FIG. 7). In particular, the call control equipment causes thevoice communications of the voice call through the first wirelessnetwork to be replicated in the connecting call through the secondwireless network, so that the mobile device simultaneously maintains thevoice communications for the voice call through both the first and thesecond wireless networks. Thus, two simultaneous voice communicationpaths of the voice call for the mobile device are maintained by the callcontrol equipment.

The call control equipment may cause the connecting call of step 706 tobe established in a number of different ways. In one embodiment, themobile device initially causes a network switching message to be sent tothe call control equipment upon detection of a predetermined condition.In response, the call control equipment initiates the connecting call tothe mobile device which causes the second wireless network to send acall initiation message (e.g. a page message for a call) to the mobiledevice. In response to the call initiation message, the mobile deviceanswers the connecting call by causing a call answering message (e.g. apage response message) to be sent to the second wireless network. In analternative embodiment, the call control equipment initiates theconnecting call without the need to receive any network switchingmessage from the mobile device. In yet another alternative embodiment,the mobile device is the entity that initiates the connecting call tothe call control equipment by sending a call initiation message to thesecond wireless network, where the call control equipment automaticallyanswers the connecting call.

Either way, the call control equipment and mobile device “automatically”and “silently” perform the activities necessary in step 706 of FIG. 7for calling or answering the connecting call. Put another way, theactivities in step 706 may be performed so as to be transparent to theend user of the mobile device. Alternatively, the mobile device maycause a user input, prompt to be visually displayed in its visualdisplay (or invoke a “call ringing” at the mobile device) for end userselection of whether the alternative (second) wireless network should beutilized. If the alternative wireless network is selected by the enduser, the mobile device causes the connecting call to be establishedwith the call control equipment. If the alternative wireless network isnot selected by the end user, the mobile device does not cause theconnecting call to be established with the call control equipment (i.e.the mobile device remains on the first wireless network).

As indicated earlier, the connecting call of step 706 may be establishedin response to identifying a predetermined condition. The predeterminedcondition may be, for example, a poor signal condition between themobile device and the wireless network (e.g. 802.11 network). As anotherexample, the predetermined condition may be a predetermined signaldetection of the wireless network (e.g. 802.11 network). That is, themere detection of the availability of the second wireless network may besufficient for the establishment of the connecting call with the callcontrol equipment. As yet another example, the predetermined conditionmay be a user input signal detected at the mobile device. Specifically,the mobile device may visually display a user input prompt or an optionfor the end user to select the alternative (second) wireless networkwhen it becomes available; the end user selection of this option is theuser input signal which triggers the connecting call to the call controlequipment. Note that the predetermined condition is preferablyidentified and acted upon at the mobile device, but may alternatively beidentified and acted upon at the call control equipment.

At some point in time, the call control equipment may completely switchthe audio paths (both receive and transmit paths) from the originalvoice call (i.e. through the first wireless network) to the connectingcall (i.e. through the second wireless network). This may be done in aquick and abrupt fashion or, alternatively, in a gradual fashion wherethe audio signals of both calls are first mixed and then subsequentlygradually decreased in volume (to/from the first wireless network) andcorrespondingly increased in volume (to/from the second wirelessnetwork) until fully switched. Such techniques may be performed by thecall control equipment or alternatively by the mobile device.Thereafter, the connection portion of the voice call from the callcontrol equipment to the mobile device through the first wirelessnetwork is terminated. When this happens, the one or more trafficchannels with the first wireless network are terminated. The callcontrol equipment may, for example, initiate the termination of theconnection portion of the original call.

FIG. 8 is a block diagram of a communication system 800 which includes amobile communication device 802. Mobile device 802 may be utilized inthe techniques of the present application as described above. As shown,mobile device 802 is adapted to communicate with a wireless local areanetwork (WLAN) 890. Also as shown, mobile device 802 is adapted tocommunicate with a wireless communication network 104 which is acellular telecommunications network. In the embodiment shown in FIG. 8,wireless network 804 is configured in accordance with General PacketRadio Service (GPRS) and a Global Systems for Mobile (GSM) technologies.However, any suitable type of network communication protocols may beutilized. For example, the network may be based on code divisionmultiple access (CDMA) or other suitable technologies. As anotherexample, the network may be based on an Integrated Dispatch EnhancedNetwork (iDEN) which is a high-capacity digital trunked radio systemproviding integrated voice and data services.

For wireless communication with wireless network 804, mobile device 802utilizes radio frequency (RF) transceiver circuitry 808 a and an antenna810 a. For wireless communication with WLAN 890, mobile device 802utilizes RF transceiver circuitry 808 b and an antenna 810 b. With suchconfiguration, mobile device 802 may be referred to as a “dual mode”communication device. Although shown in FIG. 8 as having separate andindependent transceiver components, at least some portions or componentsof these otherwise different transceivers may be shared where possible.

In the embodiment shown, mobile device 802 includes a visual display812, a keyboard 814, and perhaps one or more auxiliary user interfaces(UI) 816, each of which are coupled to a controller 806. Controller 806is further coupled to radio frequency (RF) transceiver circuitry 808 aand an antenna 810 a, as well as to RF transceiver circuitry 808 b andan antenna 810 b. Typically, controller 806 is embodied as a centralprocessing unit (CPU) which runs operating system software in a memorycomponent (not shown). Controller 806 will normally control overalloperation of mobile device 802, whereas signal processing operationsassociated with communication functions are typically performed in theRF transceiver circuitry. Controller 806 interfaces with device display812 to display received information, stored information, user inputs,and the like. Keyboard 814, which may be a telephone type keypad or fullalphanumeric keyboard, is normally provided for entering data forstorage in mobile device 802, information for transmission to network804, a telephone number to place a telephone call, commands to beexecuted on mobile device 802, and possibly other or different userinputs.

Mobile device 802 sends communication signals to and receivescommunication signals over wireless links. For communication withwireless network 804, RF transceiver circuitry 808 a performs functionssimilar to those of base station 818 and base station controller 820,including for example modulation/demodulation and possiblyencoding/decoding and encryption/decryption. It is also contemplatedthat RF transceiver circuitry 808 a may perform certain functions inaddition to those performed by base station controller 820. It will beapparent to those skilled in art that RF transceiver circuitry 808 awill be adapted to particular wireless network or networks in whichmobile device 802 is intended to operate.

Mobile device 802 includes a battery interface 834 for receiving one ormore rechargeable batteries 832. Battery 832 provides electrical powerto electrical circuitry in mobile device 802, and battery interface 834provides for a mechanical and electrical connection for battery 832.Battery interface 834 is coupled to a regulator 836 which regulatespower to the device. When mobile device 802 is fully operational, an RFtransmitter of RF transceiver circuitry 808 a is typically keyed orturned on only when it is sending to network, and is otherwise turnedoff to conserve resources. Similarly, an RF receiver of RF transceivercircuitry 808 a is typically periodically turned off to conserve poweruntil it is needed to receive signals or information (if at all) duringdesignated time periods.

Mobile device 802 operates using a Subscriber Identity Module (SIM) 840which is connected to or inserted in mobile device 802 at a SIMinterface 842. SIM 840 is one type of a conventional “smart card” usedto identify an end user (or subscriber) of mobile device 802 and topersonalize the device, among other things. Without SIM 840, the mobiledevice terminal is not fully operational for communication throughwireless network 804. By inserting SIM 840 into mobile device 802, anend user may have access to any and all of his/her subscribed services.SIM 840 generally includes a processor and memory for storinginformation. Since SIM 840 is coupled to SIM interface 842, it iscoupled to controller 806 through communication lines 844. In order toidentify the subscriber, SIM 840 contains some user parameters such asan International Mobile Subscriber Identity (IMSI). An advantage ofusing SIM 840 is that end users are not necessarily bound by any singlephysical mobile device. SIM 840 may store additional user informationfor the mobile device as well, including datebook (or calendar)information and recent call information.

Mobile device 802 may consist of a single unit, such as a datacommunication device, a cellular telephone, a multiple-functioncommunication device with data and voice communication capabilities, apersonal digital assistant (PDA) enabled for wireless communication, ora computer incorporating an internal modem. Alternatively, mobile device802 may be a multiple-module unit comprising a plurality of separatecomponents, including but in no way limited to a computer or otherdevice connected to a wireless modem. In particular, for example, in themobile device block diagram of FIG. 8, RF transceiver circuitry 808 aand antenna 810 a may be implemented as a radio modem unit that may beinserted into a port on a laptop computer. In this case, the laptopcomputer would include display 812, keyboard 814, one or more auxiliaryUIs 816, and controller 806 embodied as the computer's CPU. It is alsocontemplated that a computer or other equipment not normally capable ofwireless communication may be adapted to connect to and effectivelyassume control of RF transceiver circuitry 808 a and antenna 810 a of asingle-unit device such as one of those described above. Such a mobiledevice 802 may have a more particular implementation as described laterin relation to the mobile device of FIG. 9.

Using RF transceiver circuitry 808 a, mobile device 802 communicates inand through wireless communication network 804. In the embodiment ofFIG. 8, wireless network 804 is configured in accordance with GSM andGPRS technologies. Wireless network 804 includes a base stationcontroller (BSC) 820 with an associated tower station 818, a MobileSwitching Center (MSC) 822, a Home Location Register (HLR) 832, aServing GPRS Support Node (SGSN) 826, and a Gateway GPRS Support Node(GGSN) 828. MSC 822 is coupled to BSC 820 and to a landline network,such as a Public Switched Telephone Network (PSTN) 824. SGSN 826 iscoupled to BSC 820 and to GGSN 828, which is in turn coupled to a publicor private data network 830 (such as the Internet). HLR 832 is coupledto MSC 822, SGSN 826, and GGSN 828.

Station 818 is a fixed transceiver station, and station 818 and BSC 820are together referred to herein as the fixed transceiver equipment. Thefixed transceiver equipment provides wireless network coverage for aparticular coverage area commonly referred to as a “cell”. The fixedtransceiver equipment transmits communication signals to and receivescommunication signals from mobile devices within its cell via station818. The fixed transceiver equipment normally performs such functions asmodulation and possibly encoding and/or encryption of signals to betransmitted to the mobile device in accordance with particular, usuallypredetermined, communication protocols and parameters, under control ofits controller. The fixed transceiver equipment similarly demodulatesand possibly decodes and decrypts, if necessary, any communicationsignals received from mobile device 802 within its cell. Communicationprotocols and parameters may vary between different networks. Forexample, one network may employ a different modulation scheme andoperate at different frequencies than other networks.

For all mobile device's 802 registered with a network operator,permanent data (such as mobile device 802 user's profile) as well astemporary data (such as mobile device's 802 current location) are storedin HLR 832. In case of a voice call to mobile device 802, HLR 832 isqueried to determine the current location of mobile device 802. AVisitor Location Register (VLR) of MSC 822 is responsible for a group oflocation areas and stores the data of those mobile devices that arecurrently in its area of responsibility. This includes parts of thepermanent mobile device data that have been transmitted from HLR 832 tothe VLR for faster access. However, the VLR of MSC 822 may also assignand store local data, such as temporary identifications. Optionally, theVLR of MSC 822 may be enhanced for more efficient co-ordination of GPRSand non-GPRS services and functionality (e.g. paging forcircuit-switched calls which may be performed more efficiently via SGSN826, and combined GPRS and non-GPRS location updates).

SGSN 826 is at the same hierarchical level as MSC 822 and keeps track ofthe individual locations of mobile devices. SGSN 826 also performssecurity functions and access control. GGSN 828 provides interworkingwith external packet-switched networks and is connected with SGSNs (suchas SGSN 826) via an IP-based GPRS backbone network. SGSN 826 performsauthentication and cipher setting procedures based on the samealgorithms, keys, and criteria as in existing GSM. In conventionaloperation, cell selection may be performed autonomously by mobile device802 or by the fixed transceiver equipment instructing mobile device 802to select a particular cell. Mobile device 802 informs wireless network804 when it reselects another cell or group of cells, known as a routingarea.

In order to access GPRS services, mobile device 802 first makes itspresence known to wireless network 804 by performing what is known as aGPRS “attach”. This operation establishes a logical link between mobiledevice 802 and SGSN 826 and makes mobile device 802 available toreceive, for example, pages via SGSN, notifications of incoming data, orSMS messages over GPRS. In order to send and receive GPRS data, mobiledevice 802 assists in activating the packet data address that it wantsto use. This operation makes mobile device 802 known to GGSN 828;interworking with external data networks may thereafter commence. Userdata may be transferred transparently between mobile device 802 and theexternal data networks using, for example, encapsulation and tunneling.Data packets are equipped with GPRS-specific protocol information andtransferred between mobile device 802 and GGSN 828.

FIG. 9 is a more detailed diagram of a preferred mobile device of FIG.8, namely a mobile station 902. Mobile station 902 is preferably atwo-way communication device having at least voice and advanced datacommunication capabilities, including the capability to communicate withother computer systems. Depending on the functionality provided bymobile station 902, it may be referred to as a data messaging device, atwo-way pager, a cellular telephone with data messaging capabilities, awireless Internet appliance, or a data communication device (with orwithout telephony capabilities).

As shown in FIG. 9, mobile station 902 is adapted to wirelesslycommunicate with WLAN 992. Also as shown, mobile station 902 is adaptedto wirelessly communicate with cellular base station transceiver systems900. For communication with cellular networks, mobile station 902utilizes a communication subsystem 911. For communication with WLANs,mobile station 902 utilizes an additional communication subsystem 990which has the same structural components as communication subsystem 911.With such configuration, mobile station 902 may be referred to as a“dual mode” mobile station. Although shown in FIG. 9 as having separateand independent subsystems, at least some portions or components ofthese otherwise different subsystems may be shared where possible.

Communication subsystem 911, which includes a receiver 912, atransmitter 914, and associated components, such as one or more(preferably embedded or internal) antenna elements 916 and 918, localoscillators (LOs) 913, and a processing module such as a digital signalprocessor (DSP) 920. Communication subsystem 911 is analogous to RFtransceiver circuitry 808 a and antenna 810 a shown in FIG. 8. As willbe apparent to those skilled in field of communications, particulardesign of communication subsystem 911 depends on the communicationnetwork in which mobile station 902 is intended to operate.

Mobile station 902 may send and receive communication signals over thecellular network after required network procedures have been completed.Signals received by antenna 916 through the network are input toreceiver 912, which may perform such common receiver functions as signalamplification, frequency down conversion, filtering, channel selection,and like, and in example shown in FIG. 9, analog-to-digital (A/D)conversion. A/D conversion of a received signal allows more complexcommunication functions such as demodulation and decoding to beperformed in DSP 920. In a similar manner, signals to be transmitted areprocessed, including modulation and encoding, for example, by DSP 920.These DSP-processed signals are input to transmitter 914 fordigital-to-analog (D/A) conversion, frequency up conversion, filtering,amplification and transmission over communication network via antenna918. DSP 920 not only processes communication signals, but also providesfor receiver and transmitter control. For example, the gains applied tocommunication signals in receiver 912 and transmitter 914 may beadaptively controlled through automatic gain control algorithmsimplemented in DSP 920.

For communications with a cellular network, network access is associatedwith a subscriber or user of mobile station 902, and therefore mobilestation 902 requires a Subscriber Identity Module or “SIM” card 962 tobe inserted in a SIM interface 964 in order to operate in the network.SIM 962 includes those features described in relation to FIG. 8. Mobilestation 902 is a battery-powered device so it also includes a batteryinterface 954 for receiving one or more rechargeable batteries 956. Sucha battery 956 provides electrical power to most if not ail electricalcircuitry in mobile station 902, and battery interface 954 provides fora mechanical and electrical connection for it. The battery interface 954is coupled to a regulator (not shown) which provides power V+ to all ofthe circuitry.

Mobile station 902 includes a microprocessor 938 (which is oneimplementation of controller 806 of FIG. 8) which controls overalloperation of mobile station 902. Communication functions, including atleast data and voice communications, are performed through communicationsubsystem 911. Techniques of the present application are primarilyperformed through computer instructions which microprocessor 938 (and/orDSP 920) executes. Microprocessor 938 also interacts with additionaldevice subsystems such as a display 922, a flash memory 924, a randomaccess memory (RAM) 926, auxiliary input/output (I/O) subsystems 928, aserial port 930, a keyboard 932, a speaker 934, a microphone 936, ashort-range communications subsystem 940, and any other devicesubsystems generally designated at 942. Some of the subsystems shown inFIG. 9 perform communication-related functions, whereas other subsystemsmay provide “resident” or on-device functions. Notably, some subsystems,such as keyboard 932 and display 922, for example, may be used for bothcommunication-related functions, such as entering a text message fortransmission over a communication network, and device-resident functionssuch as a calculator or task list. Operating system software used bymicroprocessor 938 is preferably stored in a persistent store such asflash memory 924, which may alternatively be a read-only memory (ROM) orsimilar storage element (not shown). Those skilled in the art willappreciate that the operating system, specific device applications, orparts thereof, may be temporarily loaded into a volatile store such asRAM 926.

Microprocessor 938, in addition to its operating system functions,preferably enables execution of software applications on mobile station902. A predetermined set of applications which control basic deviceoperations, including at least data and voice communicationapplications, will normally be installed on mobile station 902 duringits manufacture. A preferred application which is loaded onto mobilestation 902 may be a personal information manager (PIM) applicationhaving the ability to organize and manage data items relating to e-mailmessages and voicemail messages, as well as calendar data. Naturally,one or more memory stores are available on mobile station 902 and SIM952 to facilitate storage of PIM data items and other information.

The PIM application preferably has the ability to send and receive dataitems via the wireless network. In a preferred embodiment, PIM dataitems are seamlessly integrated, synchronized, and updated via thewireless network, with the mobile station user's corresponding dataitems stored and/or associated with a host computer system therebycreating a mirrored host computer on mobile station 902 with respect tosuch items. This is especially advantageous where the host computersystem is the mobile station user's office computer system. Additionalapplications may also be loaded onto mobile station 902 through network,an auxiliary I/O subsystem 928, serial port 930, short-rangecommunications subsystem 940, or any other suitable subsystem 942, andinstalled by a user in RAM 926 or preferably a non-volatile store (notshown) for execution by microprocessor 938.

In a data communication mode, a received signal such as a text message(e.g. a short message service or SMS message), an e-mail message, or webpage download will be processed by communication subsystem 911 and inputto microprocessor 938. Microprocessor 938 will preferably furtherprocess the signal for output to display 922 or alternatively toauxiliary I/O device 928. A user of mobile station 902 may also composedata items, such as e-mail messages, for example, using keyboard 932 inconjunction with display 922 and possibly auxiliary I/O device 928.Keyboard 932 is preferably a complete alphanumeric keyboard and/ortelephone-type keypad. These composed items may be transmitted over acommunication network through communication subsystem 911. For voicecommunications, the overall operation of mobile station 902 issubstantially similar, except that the received signals would be outputto speaker 934 and signals for transmission would be generated bymicrophone 936. Alternative voice or audio I/O subsystems, such as avoice message recording subsystem, may also be implemented on mobilestation 902. Although voice or audio signal output is preferablyaccomplished primarily through speaker 934, display 922 may also be usedto provide an indication of the identity of a calling party, duration ofa voice call, or other voice call related information, as some examples.

Serial port 930 in FIG. 9 is normally implemented in a personal digitalassistant (PDA)-type communication device for which synchronization witha user's desktop computer is a desirable, albeit optional, component.Serial port 930 enables a user to set preferences through an externaldevice or software application and extends the capabilities of mobilestation 902 by providing for information or software downloads to mobilestation 902 other than through a wireless communication network. Thealternate download path may, for example, be used to load an encryptionkey onto mobile station 902 through a direct and thus reliable andtrusted connection to thereby provide secure device communication.

Short-range communications subsystem 940 of FIG. 9 is an additionaloptional component which provides for communication between mobilestation 902 and different systems or devices, which need not necessarilybe similar devices. For example, subsystem 940 may include an infrareddevice and associated circuits and components, or a Bluetooth™communication module to provide for communication with similarly-enabledsystems and devices. Bluetooth™ is a registered trademark of BluetoothSIG, Inc.

FIG. 10 is a block diagram illustration of pertinent components of callcontrol equipment 112 for use in the present application. Call controlequipment 112 of FIG. 10 includes a call control server 1002 which has awireless network interface 1004, an IP network interface 1006, and atelephone landline network or public branch exchange (PBX) interface1008. Call control server 112 is the entity which contains the primarylogic for control and processing in accordance with the presentapplication. The functionality of call control server 1002 isimplemented using computer instructions stored in memory which areexecuted by one or more processors (e.g. a microprocessor) within server1002. This functionality has been described previously in variousembodiments described in relation to FIGS. 1-5 and 7 above. IP networkinterface 1006 of call control equipment 112 is used for communicationwith the 802.11 wireless network through an IP network (e.g. theInternet and/or Intranet), where conventional VoIP communicationprotocols may be utilized. Wireless network interface 1004 is used forcommunication with cellular network, where conventional cellular networkprotocols (e.g. SS7 signalling etc.) may be utilized for control andinformation communication. Finally, PBX interface 1002 is used forfacilitating incoming or outgoing calls involving communicationterminals over the landline telephone network. Note that, depending onthe specific implementation, call control equipment 112 may only needonly some of these interfaces 1004, 1006, and 1008.

Thus, methods and apparatus for providing a seamless switching of voicecalls between different wireless networks have been described. Oneillustrative method for use by a mobile device of the presentapplication includes the steps of maintaining voice communications for avoice call with a communication terminal through call control equipment,the voice call involving a traffic channel established between a firstwireless network and the mobile device using a first transceiver portionwhich operates in accordance with the first wireless network; causing aconnecting call to be established with the communication terminalthrough the call control equipment based on identifying a predeterminedcondition, the connecting call involving a traffic channel establishedbetween a second wireless network and the mobile device using a secondtransceiver portion which operates in accordance with the secondwireless network; and after the connecting call is established,maintaining voice communications for the voice call over the trafficchannel established between the second wireless network and the mobiledevice. In a preferred embodiment, one of the first and the secondwireless networks is operative in accordance with a cellulartelecommunications network and the other one of the first and the secondwireless networks is operative in accordance with an 802.11 basedwireless network. A computer program product of the present applicationincludes a storage medium and computer instructions stored on thestorage medium which are executable by one or more processors of themobile device for performing the method as described. A mobile device ofthe present application includes one or more processors and one or morewireless transceivers coupled to the one or more processors, where theone or more wireless transceivers include a first transceiver portionoperative in accordance with a first wireless network and a secondtransceiver portion operative in accordance with a second wirelessnetwork. The one or more processors of the mobile device are operativeto perform the method as described.

An illustrative method for use by call control equipment of the presentapplication includes the steps of facilitating an establishment of avoice call between a mobile device and a communication terminal throughthe call control equipment, the voice call involving a traffic channelestablished between a first wireless network and the mobile device;causing a connecting call to be established between the call controlequipment and the mobile device during the voice call, the connectingcall involving a traffic channel established between a second wirelessnetwork and the mobile device; and causing the connecting call to beconnected with the voice call so that voice communications for the voicecall are maintained over the traffic channel between the second wirelessnetwork and the mobile device. In a preferred embodiment, one of thefirst and the second wireless networks is operative in accordance with acellular telecommunications network and the other one of the first andthe second wireless networks is operative in accordance with an 802.11based wireless network. A computer program product of the presentapplication includes a storage medium and computer instructions storedon the storage medium which are executable by one or more processors ofthe call control equipment for performing the method as described. Thecall controller server of the present application includes one or moreprocessors, memory coupled to the one or more processors, and computerinstructions stored in the memory, where the computer instructions areexecutable by the one or more processors to perform the method asdescribed.

The above-described embodiments of the present application are intendedto be examples only. For example, one of the wireless networks mayoperate in accordance with Wi-MAX technology, which is based on the IEEE802.16 Air Interface Standard for fixed wireless broadband accesssystems employing a point-to-multipoint (PMP) architecture. Those ofskill in the art may effect alterations, modifications and variations tothe particular embodiments without departing from the scope of theapplication.

1. A method for use by call control equipment in switching communicationoperations for a mobile communication device between first and secondwireless networks, the method comprising the acts of: receiving, at thecall control equipment, a call request for a call from a calling partyto a mobile communication device which operates in one of the firstwireless network and the second wireless network, where the call requestwas initiated with use of a first identification number of the mobilecommunication device which identifies the mobile communication device inthe first wireless network; in response to receiving the call requestwhen the mobile communication device is operating in the first wirelessnetwork: causing the call to be connected through the call controlequipment to the mobile communication device in the first wirelessnetwork with use of the first identification number of the mobilecommunication device which identifies the mobile communication device inthe first wireless network; after the call is connected, in response toa predetermined condition indicative of a switching of communicationoperation of the mobile communication device from the first wirelessnetwork to the second wireless network, causing a connecting call to beestablished with the mobile communication device in the second wirelessnetwork via the call control equipment; in response to receiving thecall request when the mobile communication device is operating in thesecond wireless network: causing the call to be connected through thecall control equipment to the mobile communication device in the secondwireless network with use of a second identification number whichidentifies the mobile communication device in the second wirelessnetwork; and after the call is connected, in response to identifying apredetermined condition indicative of a switching of communicationoperation of the mobile communication device from the second wirelessnetwork to the first wireless network, causing a connecting call to beestablished with the mobile communication device in the first wirelessnetwork via the call equipment.
 2. The method of claim 1, wherein one ofthe first and the second wireless networks is operative in accordancewith a cellular telecommunications network and the other one of thefirst and the second wireless networks is operative in accordance withan 802.11 based wireless network.
 3. The method of claim 1, wherein thefirst wireless network is operative in accordance with a first cellulartelecommunications network and the second wireless network is operativein accordance with a second cellular telecommunications networkdifferent from the first cellular telecommunications network.
 4. Themethod of claim 1, wherein the act of causing the connecting call to beestablished comprises: initiating the connecting call with the mobilecommunication device.
 5. The method of claim 1, wherein the act ofcausing the connecting call to be established further comprises:receiving a network switching message from the mobile communicationdevice; and initiating the connecting call with the mobile communicationdevice in response to the network switching message from the mobilecommunication device.
 6. The method of claim 1, wherein the act ofcausing the connecting call to be established further comprises:receiving the connecting call from the mobile communication device; andcausing the connecting call with the mobile communication device to beanswered.
 7. The method of claim 1, which is embodied in a computerprogram product comprising a computer readable medium and computerinstructions stored in the computer readable medium for executing theacts of the method.
 8. Call control equipment, comprising: one or moreprocessors; memory coupled to the one or more processors; computerinstructions stored in the memory; the computer instructions beingexecutable by the one or more processors for: receiving a call requestfor a call from a calling party to a mobile communication device whichoperates in one of a first wireless network and a second wirelessnetwork, where the call request was initiated with use of a firstidentification number of the mobile communication device whichidentifies the mobile communication device in the first wirelessnetwork; in response to receiving the call request when the mobilecommunication device is operating in the first wireless network: causingthe call to be connected through the call control equipment to themobile communication device in the first wireless network with use ofthe first identification number which identifies the mobilecommunication device in the first wireless network; after the call isconnected, in response to a predetermined condition indicative of aswitching of communication operation of the mobile communication devicefrom the first wireless network to the second wireless network, causinga connecting call to be established with the mobile communication devicein the second wireless network via the call control equipment; inresponse to receiving the call request when the mobile communicationdevice is operating in the second wireless network: causing the call tobe connected through the call control equipment to the mobilecommunication device in the second wireless network with use of a secondidentification number which identifies the mobile communication devicein the second wireless network; and after the call is connected, inresponse to identifying a predetermined condition indicative of aswitching of communication operation of the mobile communication devicefrom the second wireless network to the first wireless network, causinga connecting call to be established with the mobile communication devicein the first wireless network via the call equipment.
 9. The callcontrol equipment of claim 8, wherein one of the first and the secondwireless networks is operative in accordance with a cellulartelecommunications network and the other one of the first and the secondwireless networks is operative in accordance with an 802.11 basedwireless network.
 10. The call control equipment of claim 8, wherein thefirst wireless network is operative in accordance with a first cellulartelecommunications network and the second wireless network is operativein accordance with a second cellular telecommunications networkdifferent from the first cellular telecommunications network.
 11. Thecall control equipment of claim 8, further comprising: merging theconnecting call with the call.
 12. The call control equipment of claim8, wherein causing the connecting call to be established furthercomprises: receiving a network switching message from the mobilecommunication device; and initiating the connecting call with the mobilecommunication device in response to the network switching message fromthe mobile communication device.
 13. The call control equipment of claim8, wherein causing the connecting call to be established furthercomprises: receiving the connecting call from the mobile communicationdevice; and causing the connecting call with the mobile communicationdevice to be answered.
 14. The call control equipment of claim 8,wherein the step of causing the connecting call to be connected to thevoice call comprises establishing a conference call type connection withthe voice call.
 15. The call control equipment of claim 8, wherein thecall control equipment comprises a mobile branch exchange.
 16. Acommunication system, comprising: a wireless local area network (WLAN);a cellular telecommunications network; a plurality of mobilecommunication devices operative for communications in the WLAN and thecellular telecommunications network; call control equipment which isoperative to: receive a call request for a call from a calling party toa mobile communication device operating in one of the WLAN and thecellular telecommunications network, where the call request wasinitiated with use of a first identification number of the mobilecommunication device which identifies the mobile communication device inthe WLAN; in response to receiving the call request when the mobilecommunication device is operating in the WLAN: cause the call to beconnected through the call control equipment to the mobile communicationdevice in the WLAN with use of the first identification number of themobile communication device which identifies the mobile communicationdevice in the WLAN; after the call is connected, in response to apredetermined condition indicative of a switching of communicationoperation of the mobile communication device from the WLAN to thecellular telecommunications network, cause a connecting call to beestablished with the mobile communication device in the cellulartelecommunications network via the call control equipment; in responseto receiving the call request when the mobile communication device isoperating in the cellular telecommunications network: cause the call tobe connected through the call control equipment to the mobilecommunication device in the cellular telecommunications network with useof a second identification number which identifies the mobilecommunication device in the cellular telecommunications network; andafter the call is connected, in response to identifying a predeterminedcondition indicative of a switching of communication operation of themobile communication device from the cellular telecommunications networkto the WLAN, cause a connecting call to be established with the mobilecommunication device in the WLAN via the call equipment.
 17. Thecommunication system of claim 16, wherein causing the connecting call tobe established comprises: initiating the connecting call with the mobilecommunication device.
 18. The communication system of claim 16, whereincausing the connecting call to be established further comprises:receiving a network switching message from the mobile communicationdevice; and initiating the connecting call with the mobile communicationdevice in response to the network switching message from the mobilecommunication device.
 19. The communication system of claim 16, whereincausing the connecting call to be established further comprises:receiving the connecting call from the mobile communication device; andcausing the connecting call with the mobile communication device to beanswered.
 20. A communication system, comprising: a cellulartelecommunications network; a wireless local area network (WLAN); aplurality of mobile communication devices operative for communicationsin the cellular telecommunications network and the WLAN; call controlequipment which is operative to: receive a call request for a call froma calling party to a mobile communication device operating in one of thecellular telecommunications network and the WLAN, where the call requestwas initiated with use of a first identification number which identifiesthe mobile communication device in the cellular telecommunicationsnetwork; in response to receiving the call request when the mobilecommunication device is operating in the cellular telecommunicationsnetwork: cause the call to be connected through the call controlequipment to the mobile communication device in the cellulartelecommunications network with use of the first identification numberwhich identifies the mobile communication device in the cellulartelecommunications network; after the call is connected, in response toa predetermined condition indicative of a switching of communicationoperation of the mobile communication device from the cellulartelecommunications network to the WLAN, cause a connecting call to beestablished with the mobile communication device in the WLAN via thecall control equipment; in response to receiving the call request whenthe mobile communication device is operating in the WIAN: cause the callto be connected through the call control equipment to the mobilecommunication device in the WLAN with use of a second identificationnumber which identifies the mobile communication device in the WLAN; andafter the call is connected, in response to identifying a predeterminedcondition indicative of a switching of communication operation of themobile communication device from the WLAN to the cellulartelecommunications network, cause a connecting call to be establishedwith the mobile communication device in the cellular telecommunicationsnetwork via the call equipment.